The Pantheon+ Analysis: Forward-Modeling the Dust and Intrinsic Colour Distributions of Type Ia Supernovae, and Quantifying their Impact on Cosmological Inferences

Popovic, Brodie; Brout, D.; Keßler, R.; Scolnic, D.

doi:10.48550/arxiv.2112.04456

Cited by 13 publications

(37 citation statements)

References 31 publications

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“…With this mind, it is natural to suspect that the colour correction in this case is predominantly driven by dust extinction. This picture is consistent with the probabilistic model of SN colours used by Popovic et al (2021) for which the red tail of the observed colour distribution arises entirely from reddening due to dust. Following this interpretation, we conclude that a low, nearly Planckian value of the Hubble constant (or a longer distance scale) obtained in our analysis for c ref ∼ < −0.1 results most likely from a stronger dust extinction and thus higher intrinsic brightness (∆m ≈ 0.17 for c ref = −0.13 and model B) of SNe in the calibration sample than in the baseline model.…”

Section: Discussionsupporting

confidence: 88%

“…The reference colours required to obtain the Planck value of the Hubble constant coincide with the blue end of the observed colour distribution in the cosmological and calibration sample. Interestingly, the reference colour for the preferred model B is within the 1σ range of the intrinsic colour distribution derived from the Pantheon+ SN sample (Popovic et al 2021).…”

Section: Hubble Constantsupporting

confidence: 62%

“…4, the Hubble constant tension decreases to just 1σ when the adopted reference colour in eq. ( 8) is the mean intrinsic colour of type Ia SNe, as measured recently from the Pantheon+ sample (Popovic et al 2021). It is also important to notice that the relative colour c − c ref in the calibration sample becomes strictly positive (see Fig.…”

Section: Discussionmentioning

confidence: 72%

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Intrinsic tension in the supernova sector of the local Hubble constant measurement and its implications

Wojtak

Hjorth

2022

Monthly Notices of the Royal Astronomical Society

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We reanalyse observations of type Ia supernovae (SNe) and Cepheids used in the local determination of the Hubble constant and find strong evidence that SN standardisation in the calibration sample (galaxies with observed Cepheids) require a steeper slope of the colour correction than in the cosmological sample (galaxies in the Hubble flow). The colour correction in the calibration sample is consistent with being entirely due to an extinction correction due to dust with properties similar to that of the Milky Way (RB ≈ 4.6 ± 0.4) and there is no evidence for intrinsic scatter in the SN peak magnitudes. An immediate consequence of this finding is that the local measurement of the Hubble constant becomes dependent on the choice of SN reference colour, i.e. the colour of an unreddened SN. Specifically, the Hubble constant inferred from the same observations decreases gradually with the reference colour assumed in the SN standardisation. We recover the Hubble constant measured by SH0ES for the standard choice of reference colour (SALT2 colour parameter c = 0) while for a reference colour which coincides with the blue end of the observed SN colour distribution (c ≈ −0.13), the Hubble constant from Planck observations of the CMB (assuming a flat ΛCDM cosmological model) is recovered. These results are intriguing in that they may provide an avenue for resolving the Hubble tension. However, since there is no obvious physical basis for the differences in colour corrections in the two SN samples, the origin of these require further investigations.

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Section: Discussionsupporting

confidence: 88%

Section: Hubble Constantsupporting

confidence: 62%

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Intrinsic tension in the supernova sector of the local Hubble constant measurement and its implications

Wojtak

Hjorth

2022

Monthly Notices of the Royal Astronomical Society

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“…A brief overview of SNANA is as follows: 1) fluxes are generated from a source model, with noise and detection characterized in survey-specific methods alongside a rest-frame SED for each epoch that is subject to cosmological and galactic effects, 2) the SED is integrated for each filter to obtain broadband fluxes, which are further subjected to surveyspecific measurement noise, and 3) candidate logic and spectroscopic identification efficiencies are applied. For this paper, we take our Pan-theon+ simulation inputs from Brout et al (2022), a brief overview of which is presented in Table 2 of Popovic et al (2021a).…”

Section: Simulationsmentioning

confidence: 99%

“…Type Ia supernovae (SNe Ia) were used to discover the acceleration of the universe (Riess et al 1998;Perlmutter et al 1999), and are now being used to make some of the most precise measurements of the equation-of-state of dark energy (𝑤, e.g., Garnavich et al 1998;Suzuki et al 2012;Betoule et al 2014;Scolnic et al 2018;DES Collaboration et al 2019;Brout et al 2022) and the current expansion rate parameterized by H 0 (e.g., Freedman et al 2019;Riess et al 2021). However, recent analyses have shown that improvement of these measurements depends on a better understanding of the impact of dust around SNe Ia and how it relates to the scatter found in standardized SNe Ia brightnesses Popovic et al 2021a).…”

Section: Introductionmentioning

confidence: 99%

Constraining R$_V$ Variation Using Highly Reddened Type Ia Supernovae from the Pantheon+ Sample

Rose¹,

Popovic²,

Scolnic³

et al. 2022

Preprint

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Type Ia supernovae (SNe Ia) are powerful tools for measuring the expansion history of the universe, but the impact of dust around SNe Ia remains unknown and is a critical systematic uncertainty. One way to improve our empirical description of dust is to analyse highly reddened SNe Ia (𝐸 (𝐵 − 𝑉) > 0.4, roughly equivalent to the fitted SALT2 light-curve parameter 𝑐 > 0.3). With the recently released Pantheon+ sample, there are 57 SNe Ia that were removed because of their high colour alone (with colours up to 𝑐 = 1.61), which can provide enormous leverage on understanding line-of-sight 𝑅 𝑉 . Previous studies have claimed that 𝑅 𝑉 decreases with colour, though it is unclear if this is due to limited statistics, selection effects, or an alternative explanation. To test this claim, we fit two separate colour-luminosity relationships, one for the main cosmological sample (𝑐 < 0.3) and one for highly reddened (𝑐 > 0.3) SNe Ia. We find the change in the colour-luminosity coefficient to be consistent with zero. Additionally, we compare the data to simulations with different colour models, and find that the data prefers a model with a flat dependence of 𝑅 𝑉 on colour over a declining dependence. Finally, our results strongly support that line-of-sight 𝑅 𝑉 to SNe Ia is not a single value, but forms a distribution.

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The Dark Energy Survey supernova program: cosmological biases from supernova photometric classification

Vincenzi

Sullivan

Möller

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Cosmological analyses of samples of photometrically-identified type Ia supernovae (SNe Ia) depend on understanding the effects of ‘contamination’ from core-collapse and peculiar SN Ia events. We employ a rigorous analysis using the photometric classifier SuperNNova on state-of-the-art simulations of SN samples to determine cosmological biases due to such ‘non-Ia’ contamination in the Dark Energy Survey (DES) 5-year SN sample. Depending on the non-Ia SN models used in the SuperNNova training and testing samples, contamination ranges from 0.8–3.5 per cent, with a classification efficiency of 97.7–99.5 per cent. Using the Bayesian Estimation Applied to Multiple Species (BEAMS) framework and its extension BBC (‘BEAMS with Bias Correction’), we produce a redshift-binned Hubble diagram marginalised over contamination and corrected for selection effects, and use it to constrain the dark energy equation-of-state, w. Assuming a flat universe with Gaussian ΩM prior of 0.311 ± 0.010, we show that biases on w are <0.008 when using SuperNNova, with systematic uncertainties associated with contamination around 10 per cent of the statistical uncertainty on w for the DES-SN sample. An alternative approach of discarding contaminants using outlier rejection techniques (e.g., Chauvenet’s criterion) in place of SuperNNova leads to biases on w that are larger but still modest (0.015–0.03). Finally, we measure biases due to contamination on w0 and wa (assuming a flat universe), and find these to be <0.009 in w0 and <0.108 in wa, 5 to 10 times smaller than the statistical uncertainties for the DES-SN sample.

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The Pantheon+ Analysis: Forward-Modeling the Dust and Intrinsic Colour Distributions of Type Ia Supernovae, and Quantifying their Impact on Cosmological Inferences

Cited by 13 publications

References 31 publications

Intrinsic tension in the supernova sector of the local Hubble constant measurement and its implications

Intrinsic tension in the supernova sector of the local Hubble constant measurement and its implications

Constraining R$_V$ Variation Using Highly Reddened Type Ia Supernovae from the Pantheon+ Sample

The Dark Energy Survey supernova program: cosmological biases from supernova photometric classification

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